| 摘要 |
1,201,810. 810. Automatic control of current. ROBERT BOSCH G.m.b.H. Dec.21, 1967 [Dec.21, 1966], No.58208/67. Heading G3R. [Also in Division H2] A control system for a d.c. motor 10, 11, e.g. for traction comprises a semi-conductor switch (thyristor 13) for regulating the current, a control circuit 37 responsive to a reference value set on a controller 42, and a bridging contactor 19, 22 shunting the switch and controlled by a voltage dependent semi-conductor (transistor) circuit 67 connected through an integrating circuit to the output of the control circuit 37. The reference value at 42 is opposed by the voltage across a resistor 18 in series with the motor, smoothed by capacitor 64, so that the circuit 37 controls the duty ratio of thyristor 13 to keep the motor current constant, at leat during acceleration. When, as the motor nears full speed, the duty ratio approaches 100% the voltage from the integrating circuit (in 67) is sufficient to switch on the transistor circuit 67, thereby energizing 19 and closing contacts 22. Thus the motor is fully energized, but the circuit 37 continues to be activated and if, due to an increased load, the duty cycle drops, the bridging contactor is deenergized and current control re-established. The bridging contact is, however, held closed if the controller 42 is advanced to the full speed position, and also if a second integrating circuit detects very rapid switching by the circuit 37, which occurs if the motor is stalled. Rapid changes by the controller 42 in the increase current direction are delayed by RC circuit 53, 63, which is short circuited for the decrease direction by a diode 62. Motor current during "off" periods is carried by a freewheeling diode 33. The main thyristor 13 is switched off by a capacitor 26 switched by a commutating thyristor 25, 13 and 25 being triggered alternately by respective blocking oscillators 35, 36 controlled by the circuit 37. The triggering circuits 35, 36 and the control circuits 37, 67 are fully described Figs. 6 and 7 (not shown). The thyristor 13 may alternatively be a "gate controlled switch". A resistor 59 is inserted in the current feedback path when 22 is closed to compensate for the current change due to loss of voltage drops though 13. |
